Data.Task

The Task(a, b) structure represents values that depend on time. This allows one to model time-based effects explicitly, such that one can have full knowledge of when they're dealing with delayed computations, latency, or anything that can not be computed immediately.

A common use for this monad is to replace the usual Continuation-Passing Style form of programming, in order to be able to compose and sequence time-dependent effects using the generic and powerful monadic operations.

Example

varTask=require('data.task')varfs=require('fs')// read : String -> Task(Error, Buffer)functionread(path){returnnewTask(function(reject,resolve){fs.readFile(path,function(error,data){if(error)reject(error)elseresolve(data)})})}// decode : Task(Error, Buffer) -> Task(Error, String)functiondecode(task){returntask.map(function(buffer){returnbuffer.toString('utf-8')})}varintro=decode(read('intro.txt'))varoutro=decode(read('outro.txt'))// You can use `.chain` to sequence two asynchronous actions, and// `.map` to perform a synchronous computation with the eventual// value of the Task.varconcatenated=intro.chain(function(a){returnoutro.map(function(b){returna+b})})// But the implementation of Task is pure, which means that you'll// never observe the effects by using `chain` or `map` or any other// method. The Task just records the sequence of actions that you// wish to observe, and defers the playing of that sequence of actions// for your application's entry-point to call.//// To observe the effects, you have to call the `fork` method, which// takes a callback for the rejection, and a callback for the success.concatenated.fork(function(error){throwerror},function(data){console.log(data)})

Installing

The easiest way is to grab it from NPM. If you're running in a Browser environment, you can use Browserify

$ npm install data.task

Using with CommonJS

If you're not using NPM, Download the latest release, and require the data.task.umd.js file:

varTask=require('data.task')

Using with AMD

Download the latest release, and require the data.task.umd.js file:

require(['data.task'],function(Task){( ... )})

Using without modules

Download the latest release, and load the data.task.umd.js file. The properties are exposed in the global Task object:

<scriptsrc="/path/to/data.task.umd.js"></script>

Compiling from source

If you want to compile this library from the source, you'll need Git, Make, Node.js, and run the following commands:

$ git clone git://github.com/folktale/data.task.git
$ cd data.task
$ npm install
$ make bundle

This will generate the dist/data.task.umd.js file, which you can load in any JavaScript environment.

Documentation

You can read the documentation online or build it yourself:

$ git clone git://github.com/folktale/data.task.git
$ cd data.task
$ npm install
$ make documentation

Platform support

This library assumes an ES5 environment, but can be easily supported in ES3 platforms by the use of shims. Just include es5-shim :)

Licence

Copyright (c) 2013-2015 Quildreen Motta.

Released under the MIT licence.